2. HISTORY
Fungi were recognized as causative agents of
human disease earlier than bacteria (1839)
They received scanty importance due to their
benign nature of the diseases caused.
Fungal infections are however very common,
serious and even fatal.
Modern advances in treatment such as
antibiotics, steroids& immunosuppressive drugs
have led to an increase in opportunistic
pathogenic infections.
3. Introduction
Fungi are eukaryotic protista; differ from
bacteria and other prokaryotes.
1. Cell walls containing chitin (rigidity & support),
mannan & other polysaccharides
2. Cytoplasmic membrane contains ergosterols
3. Possess true nuclei with nuclear membrane &
paired chromosomes.
4. Divide asexually, sexually or by both
5. Unicellular or multicellular
4. Introduction
Simplest fungus :- Unicellular budding
yeast
Hypha :- Elongation of apical cell
produces a tubular, thread like structure
called hypha
Mycelium :- Tangled mass of hyphae is
called mycelium. Fungi producing
mycelia are called molds or filamentous
fungi.
Hyphae may be septate or non-septate
5. Classification
Fungi can be classified
Depending on cell morphology :4
types
Based on sexual spore formation: 4
classes
7. 1. Yeasts
Unicellular fungi which
reproduce by budding
On culture - produce
smooth, creamy colonies
e. g Cryptococcus
neoformans (capsulated
yeast)
8. 2. Yeast like fungi
Grow partly as yeasts and partly as
elongated cells resembling hyphae which
are called pseudohyphae.
e.g. Candida albicans
9. 3. Molds/ Filamentous fungi
Form true mycelia &
reproduce by formation
of different types of
spores.
Vegetative/ aerial
hyphae
e.g. Rhizopus, mucor
10. 4. Dimorphic fungi
Occur in 2 forms
Molds (Filaments) – 25C (soil)
Yeasts – 37C (in host tissue)
Most fungi causing systemic infections
are dimorphic:
Histoplasma capsulatum
Blastomyces dermatidis
Paracoccidioides brasiliensis
Coccidioides immitis
Penicillium marneffei
Sporothrix schenkii
11. Systematic classification
Based on sexual spore formation: 4
classes
1. Zygomycetes
2. Ascomycetes reproduce sexually
3. Basidiomycetes
4. Deuteromycetes (fungi imperfectii)
12. 1. Zygomycetes
Lower fungi
Broad, nonseptate hyphae
Asexual spores -
Sporangiospores: present
within a swollen sac- like
structure called
Sporangium
13. 1. Zygomycetes
Sexual spores -
Zygospore: a
resting, thick walled
cell in between
hyphae
e.g. Rhizopus,
Mucor, Absidia
14. 2. Ascomycetes
Includes both yeasts & filamentous fungi
Narrow, septate hyphae
Asexual spores are called conidia borne on conidiophore
15. 2. Ascomycetes
Sexual spores called
ascospores are present
within a sac like structure
called Ascus.
Several asci may be seen
within a fruiting body as seen
in Penicillium, Aspergillus
Each ascus has 4 to 8
ascospores.
16. 3. Basidiomycetes
Sexual fusion results in the formation of a
club shaped organ called base or basidium
which bear spores called basidiospores e.g.
trichosporon,malassezia
17. 4. Deuteromycetes
or Fungi imperfectii
Group of fungi whose sexual phases are
not identified.
Grow as molds as well as yeasts.
Asexual stage – conidia
e.g. Candida, Cryptococcus
18. Vegetative Structures of Fungi
Formed by the vegetative mycelia
(modification of single vegetative cells or
hyphae)
Have no reproductive value
Important in the differentiation/
identification of clinically significant fungi.
20. Vegetative Structures of
Fungi
Arthrospores –
formed by
segmentation &
condensation of
hyphae
Chlamydospores –
thick walled resting
spores
e.g. C.albicans
21. Reproduction in fungi
Sexual - formation of zygospores,
ascospores or basidiospores
Asexual reproduction – budding or fission
Asexual spores are formed on or in
specialized structures.
Vary in size, shape & colour but these
characteristics are constant for a particular
species.
22. Reproduction in fungi
Micro conidia -
Small, single
celled
Macro conidia –
Large, single or
many celled
23. Fungal Infections/ Mycoses
Superficial mycoses:
2 types: surface and cutaneous mycoses
Skin, hair & nails.
Mild but chronic disease
Deep mycoses:
2 types: subcutaneous & systemic mycoses
Caused by soil saprophytes
Infection is accidental
Range from a symptomatic infection to fatal disease
24. Superficial: Surface mycoses
Live exclusively on dead surfaces of
skin and its appendages
No contact with living tissue, hence no
inflammatory response
1. Tinea versicolor
2. Tinea nigra
3. Piedra
25. Superficial: Cutaneous mycoses
Cornified layer of skin & its appendages
Contact with living tissue, hence
inflammatory & allergic responses seen
1. Dermatophytes – skin, hair & nails
2. 3 genera - Trichophyton
Microsporum
Epidermophyton
27. Candidiasis
Caused by candida sps, forms a bridge
between superficial & deep mycoses as
it can cause cutaneous as well as
systemic infections
Can also cause opportunistic infections
28. Opportunistic infections
Pts with debilitating disease, altered
physiological state
Mainly caused by fungi which are common lab
contaminant on culture media
Aspergillus
Pencillium
Mucor
Rhizopus
Produce serious & fatal infections
29. Useful Properties of Fungi
Source of food
e.g. mushrooms
Fermentation - Production of
alcohol, bread
e.g. Sacchromyces spps
Antibiotic production
e.g. Penicillin from
Penicillium notatum
30. Useful Properties of Fungi
Ergot from Claviceps
purpurea, used to induce
uterine contractions
Vaccines for Hepatitis B –
Sacchromyces cerevisiae
